1. Field of the Invention
The invention relates to an electrical machine, in particular a direct current machine.
2. Description of the Prior Art
From International Patent Disclosure WO 2005/076442 A, an electric motor with a symmetrically disposed armature winding is known. The symmetrically disposed armature winding comprises a first coil that is wound between two arbitrary armature slots and is electrically contacted at adjacent commutator laminations. A second coil is wound between two armature slots that are in a point-symmetrical position relative to the two armature slots of the first coil, with respect to the center point of the armature shaft and is wound in the opposite direction. In the motor, the number of armature slots is equal to the number of commutator laminations. The motor has one brush each for high and low speeds as well as one common brush. The first and second coils are disposed in such a way that they are located in a symmetrical position to an axis that passes through the center point of the brush for high speeds and the center point of the rotary shaft when the brush for high speeds comes into contact with the adjacent commutator lamination and as a result short-circuits the first coil to the second coil.
The disposition of the brushes with respect to the first and second coils that are symmetrical to one another as in WO 2005/076442 has the disadvantage that one circuit conductor of each coil leads directly from the armature slot to the commutator. The term switching conductor is understood to mean that portion of a coil wire that leads from the coil to the commutator. This means that this switching conductor is fastened quasi-freely between the coil and the commutator hook. The fastened switching conductor thus blocks the space for the following switching conductors of the other coils. The result is a large winding head construction and possibly breakage at the commutator hook of the fastened switching conductor under vibrational stress, which can cause field failures.